The present invention relates to a fibrous acoustical material for reducing noise transmission, such as automotive floor insulator and automotive trunk insulating carpet, and a method for producing the fibrous acoustical material.
Today, there is a demand for the development of an acoustical material that is superior in sound insulating capability. Hitherto, there have been various acoustical materials, such as (i) a felt prepared from regenerated fibers by using a thermosetting binder (e.g., phenolic resin), (ii) a molded felt prepared by using a thermoplastic binder (e.g., polyethylene and polypropylene resins), (iii) another molded felt prepared by adding thermoplastic fibers as a binder, (iv) an acoustical material prepared by heat or cold pressing an inorganic fibrous material (e.g., glass fibers) containing a thermosetting or thermoplastic resin, and (v) a fibrous material prepared at first by mixing principal fibers (e.g., polyester fibers) with binding fibers having a lower melting point than that of the principal fibers and then by heating the resultant mixture in a manner to melt the binding fibers. This fibrous material (v) has widely been used as an acoustical material, due to its relatively high sound insulating capability. If it is required to improve heat resistance of this fibrous material, it is possible to use fibers having a high softening point as the binding fibers. With this, however, the number of contact points, at which the principal and binding fibers are held together as the result of adhesion of the binding fibers to the principal fibers, may become insufficient. This may make the fibrous material inferior in resistance to compressive force in its use as a floor insulator. If the amount of the constituent fibers of the fibrous material is increased in order to make the fibrous material satisfactory in resistance to compressive force, the fibrous material may become too heavy in weight and inferior in acoustical capability due to the increase of dynamic spring constant. Furthermore, if the fineness of the principal fibers is increased, the fibrous material may become inferior in sound absorption capability.